1. Field of the Invention
The invention relates to a device for the reversible storage of electric energy by its reversible conversion into kinetic energy in an electric motor, the electric energy being drawn from an a.c. power supply of predetermined frequency and fed back into the a.c. power supply, and also to a process for the operation of this device and to use of a brushless, electronically commutated pancake motor with permanent magnets arranged on the rotor and coreless windings arranged on the stator as an energy store in the abovementioned reversible storage of electric energy.
2. Discussion of the Prior Art
Unless otherwise specified, it is generally to be understood in conjunction with the present invention that the kinetic energy stored in an electric motor may be present both in the mechanical form and in the electrical form or as a combination and sum of these two forms of energy.
The mechanical form of the kinetic energy stored in the electric motor is stored in the rotation of the motor. The electrical form of the kinetic energy stored in the electric motor is stored in the current which flows through those parts of the stator winding which act as an induction coil or choke. It is well-known to a person skilled in the art of mechanics that the rotating rotor stores a mechanical form of kinetic energy dependent on its inertia and its rotational speed, and it is well-known to a person skilled in the art of electrical engineering that a choke or induction coil stores an electrical form of kinetic energy dependent on the current flowing through it (for further explanation it is submitted that, in contrast to this, the electric energy in a capacitor is stored in the form of potential energy, which has the effect that in an LC oscillator the electric energy is exchanged between the potential form and the kinetic form of electric energy). In conjunction with the present invention, the mechanical form and the electrical form of kinetic energy are to be regarded and considered together.
In particular for the uninterrupted feeding of a load from an a.c. power supply, it is known to use as the energy store for the reversible storage of electric energy a d.c. motor which is connected via a supply-side converter to the a.c. power supply and via a load-side converter to the load. In the case of such devices it is always necessary to provide a change-over facility, in order if need be, i.e. depending on the conditions prevailing at the a.c. power supply and at the load, to connect the load to the a.c. power supply or to the load-side converter, or to change it over. In this context it is also known to correct shortcomings of the a.c. power supply, such as deviations or distortions of voltage, waveform, frequency, phase etc., and reactions of the load on the a.c. power supply by electric energy, which is taken from the d.c. motor and fed via the supply-side converter and/or the load-side converter into the a.c. power supply or into the load, respectively.
There are, however, some cases in which this known technique cannot be used at all, or only to a restricted extent or with reservations, in particular for reasons of cost and/or for reasons of space. Such cases are to be encountered in drive technology, if very fast starting times and braking times (the latter for example for accurate positioning) are required, such as in lifts, conveyor belts, electric motor cars, robots etc.